Scientific Evidence of Evolution We have to be able to explain how we know that evolution is fact. Scientists look for evidence.
Four types of evidence that support the process of evolution.
1. Biogeographical Evidence
a) Species can look similar but live in different parts of the world, they design the same body part for the same reason, in response to the same environmental needs.
e.g dry habitat so preserve water by reducing size of leaves to needles
Compares species (biological) in different places (geographical areas)
These two species live on different continents. They have the same design to solve the problem, an extremely dry habitat.
b) Darwin noticed that animals on islands look more similar to animals on nearby islands, and different to animals on faraway islands.
(More likely to have a common ancestor with closely related islands).
These tortoises all live on different islands in the Galapagos Archipelago. They look more like each other than they look like tortoises from far away. They also look slightly different to each other which was also significant to Darwin.
2. Fossils
a) show evidence of change over time.
The fossils show that the living things that are alive now are not the same as the living things that were alive before.
Studying similarities and differences in body structure allows scientists to infer relationships between species. (Sometimes the external appearances however are deceptive and are a result of similar habitats, rather than ancestral links). This was all that scientists had to go for many years. A lot of the ideas were not right. There are still some good examples, like the pentadactyl limb.
5 The muscle in the bottom of the foot,the Plantaris Muscle.
The Plantaris muscle is used to grip and manipulate objects, and humans have lost the use of this muscle,even though most of us still have it. The muscle is so underdeveloped doctors use it for surgeries to replace other tissues. In fact 9% of humans are now born without this muscle.
4. Wisdom Teeth.
Early humans ate a lot of plants – and they needed to eat them quickly enough that they could eat a sufficient amount in one day to get all of the nutrients they needed. For this reason, we had an extra set of molars to make the larger mouth more productive. This was particularly essential as the body lacked the ability to sufficiently digest cellulose. As evolution made its selections, our diets changed, our jaws grew appropriately smaller, and our third molars became unnecessary. Some human populations have now all but completely stopped growing wisdom teeth, while others have almost 100% likelihood of developing them.
3 Darwin’s PointPlica semilunaris
800Px-Darwin-S-Tubercle
Darwin’s point is found in the majority of mammals, and humans are no exception. It is most likely used to help focus sounds in animals, but it no longer has a function in humans. Only 10.4% of the human population still has this visible left-over mark of our past, but it is possible that a much larger number of people carry the gene that produces it as it does not always cause the ear tubercle to appear. The point (shown in the picture above) is a small thick nodule at the junction of the upper and middle sections of the ear. 2Coccyx
Sacrum
The coccyx is the remnant of what was once a human tail. Over time we lost the need for a tail (as tree swinging was replaced by hanging out at the local water hole grunting neanderthal gossip), but we did not lose the need for the coccyx: it now functions as a support structure for various muscles and a support for a person when he sits down and leans back. The coccyx also supports the position of the anus. 1Appendix
Gray536
The appendix has no known use in modern humans and is often removed when it becomes infected. While its original use is still speculated on, most scientists agree with Darwin’s suggestion that it once helped to process the cellulose found in the leaf-rich diet that we once had. Over the course of evolution, as our diet has changed, the appendix became less useful. What is particularly interesting is that many evolutionary theorists believe that natural selection (while removing all of the abilities of the appendix) selects larger appendices because they are less likely to become inflamed and diseased. So unlike the little toe, which may eventually vanish and is equally useless, the appendix is likely to stay with us for a long time – just hanging around doing nothing.
Embryology is an example of comparative anatomy as well - embryos go through stages of development, in vertebrates it appears that embryos show the relationships of ancestral pathways as they go through foetal development. Link to diagram of vertebrate embryo's.
Who knew you had a fish stage in your embryo?
- study of proteins, amino acids,genes and DNA that species that are closely related have in common, now that scientists are able to identify chemicals at these molecular levels they can work out close relationships between species based on their chemical differences. Close relatives have similar biochemicals.
You can compare the genes located on the chromosomes of different species.
You can see the genes in common between this collection of primates, and can use the differences to establish how closely related the species are.
Studies of proteins like haemoglobin, of enzymes like cytochrome c, of immunoglobins can all show the relatedness between different species. Some proteins are so essential to life that they hardly mutate at all. These proteins are called Highly Conserved Proteins, and any change in an amino acid sequence can be traced.
Alan Wilson used these mutations to develop a Molecular Clock, which uses the rate of mutations to create a timeline for speciation. He showed that relationships between species could be constructed from changes in molecules such as proteins. The more changes there are, the further the distance in the relationship. Wilson used the sequences in the biological molecule to show that some species descend from common ancestors, the number of changes is related to time. He showed that Chimps and Humans have 99% the same sequences in our DNA, and that the time of separation from a common ancestor should be about 6 million years ago, and even more amazing, that all living humans descend from a single female ancestor that lived 60 000 years ago. (The Alan Wilson Centre is a world renowned research centre , and has excellent material about Human Evolution if you want to go there now)
New understandings from studies in this field are arriving all the time.
Scientists used to think that there was such a wide range of eye structures through out the animal kingdom that they must have developed independently. Studying genetics however has started to show that the genes for the structures of eyes are foundation genes, but how they turn on and what they do has evolved. There are some really exciting examples at this link to Learn Genetics Utah University Foundation Tool Kit genes page.
Basing an argument on Scientific Evidence is important - The theory of evolution uses separate lines of evidence from many fields to support the same argument, that species change due to natural observable processes. Stated Clearly gives some well made arguments. The video has the Same stuff that you have had in class, but a different voice to listen to.
Can fossils AND comparative anatomy both say the same thing. for example the evolution of whales.
Can complex structures like eyes actually evolve? Surely they are too hard or too soft to evolve? What about the half way eyes? Wouldn't those species just die out and not be present to evolve from? How can half working eyes give an evolutionary advantage and be successful? You'd think, but there is proof. Check out this doco, quite interesting so hang in there.
Conclusion
These are all ways that scientists have confirmed that evolution has been taking place. When you are thinking about species that might be evolving or might have evolved, your job is to think about which type of evidence can you use to find support for or against the idea that speciation has taken place.
An example of scientists using evidence to prove an evolutionary relationship is looking at teosinte corn, is it the ancestor of modern maize? What evidence would we need to find? http://maize.uga.edu/index.php?loc=ancestors
Next job, how does evolution take place?
Mechanisms of Change
Sounds flash, but really it just means what is required to make a change in a species happen?
The definition we have worked on in class is
'Evolution is a change in the allele frequency of a gene pool, over time'.
To cause evolution then, you must make a change in the allele's frequency. This just means make more of the allele or make less of the allele. If the allele becomes more or less common its frequency has changed. This change is identified as a micro evolutionary process (as compared to macro evolution which is speciation- evolution on a large scale - some people think they are the same thing just over different periods of time).
There are three main causes of change in allele frequency.
1 Natural Selection.
2 Migration.
3 Genetic Drift
A note about Mutation - without mutations you can't get different alleles for evolution to work on, so mutations are the foundation of evolution, but not a cause of change. What do you think? Is this splitting hairs?
And this website is a bit odd, the video of interest explains the features of Genetic Drift, there are a collection of videos that are a bit unpredictable, some are better than others, but the good ones are worth looking at,
a humourous lego simulation that explains the examples of Founder Effect, Bottlenecks and Genetic Drift really well
We need to look at case studies of each mechanism of change. yr 12 Bio go back to Genetic Variation and Change page.
So in summary, natural selection is what Darwin is famous for writing down , it is the mechanism that makes sure the species is adapted to do well in the habitat they live in, genetic drift affects small populations, it is just a chance event that does not favour one phenotype over another to suit the habitat, and migration is migration, an individual arrives (or leaves) to breed with the members, bringing their alleles in (or out) of the pool.
All three make something happen that changes the balance between the alleles that are in the gene pool, from one generation to the next.
One key thing to remember is that the change has to be passed on to the next generation,if it isn't passed on to the gene pool of the next generation, it isn't evolution.
Evolution relies on variation in a population. One of the main sources of variation is sexual reproduction. Sexual reproduction means that two parents contribute chromosomes to the offspring. For this to happen, reproducing adults must create a special cell with a half set of chromosomes. This sex cell is called a gamete. The process that creates a gamete is called Meiosis.
There are three features of meiosis and sexual reproduction that introduce this important variation.
1 Cross over and recombination
2 Independent assortment and segregation
3 Fertilisation of a gamete by another unique gamete.
Each of these steps needs to be clearly understood by students. So lets get some help.
Crossover is a process that only occurs in meiosis(not in mitosis). The homologous chromosomes must pair up in meiosis, and when they do, the chromatids that are lined next to each can overlap, and break off and recombine with the other chromatid. This swaps alleles from parents on to different chromosomes.
The original versions had alleles AB and ab, but after crossover one of the chromatids carries Ab, and the other carries aB. Now the offspring can get one of four possible combinations of these two alleles.
Which one it will get will depend on how the chromatids sort themselves into gametes.
Independent assortment and segregation.
This process happens independently for each pair of chromosomes, and every time it could be a different combo of chromosomes inside the gamete.
This picture shows the combinations possible from just 3 pairs of chromosomes.
Whichever one of these gametes fertilises the other gamete,the offspring will be slightly different, but based on the same parents!
Genetics and Evolution
Scientific Evidence of Evolution
We have to be able to explain how we know that evolution is fact. Scientists look for evidence.
Four types of evidence that support the process of evolution.
1. Biogeographical Evidence
a) Species can look similar but live in different parts of the world, they design the same body part for the same reason, in response to the same environmental needs.e.g dry habitat so preserve water by reducing size of leaves to needles
Compares species (biological) in different places (geographical areas)
These two species live on different continents. They have the same design to solve the problem, an extremely dry habitat.
b) Darwin noticed that animals on islands look more similar to animals on nearby islands, and different to animals on faraway islands.
(More likely to have a common ancestor with closely related islands).
These tortoises all live on different islands in the Galapagos Archipelago. They look more like each other than they look like tortoises from far away. They also look slightly different to each other which was also significant to Darwin.
2. Fossils
a) show evidence of change over time.The fossils show that the living things that are alive now are not the same as the living things that were alive before.
Interesting modern plants with fossil ancestors are the Wollemi Pine (http://www.adonline.id.au/plantevol/wollemi-pine/ ) in Australia and the Ginkgo species, (http://www.adonline.id.au/plantevol/ginkgo/) . There is scientific debate about which species these trees are related to. How can this be established? We have a Ginkgo tree on the wharenui lawn.
3 Comparative Anatomy
Studying similarities and differences in body structure allows scientists to infer relationships between species. (Sometimes the external appearances however are deceptive and are a result of similar habitats, rather than ancestral links). This was all that scientists had to go for many years. A lot of the ideas were not right. There are still some good examples, like the pentadactyl limb.Check out what that is and why the anatomy of it is important e.g at http://www.nhm.ac.uk/nature-online/evolution/what-is-the-evidence/morphology/pentadactyl-limb/
or at this page, http://www.blackwellpublishing.com/ridley/tutorials/the_evidence_for_evolution15.asp, for another explanation of the relevance of these homologous structures.
Vestigial Organs.
Then there are the organs that are present that are no longer functional. Here are 5 examples from Human Evolution.
http://listverse.com/2009/01/05/top-10-signs-of-evolution-in-modern-man/
5 The muscle in the bottom of the foot,the Plantaris Muscle.
The Plantaris muscle is used to grip and manipulate objects, and humans have lost the use of this muscle,even though most of us still have it. The muscle is so underdeveloped doctors use it for surgeries to replace other tissues. In fact 9% of humans are now born without this muscle.
4. Wisdom Teeth.
Early humans ate a lot of plants – and they needed to eat them quickly enough that they could eat a sufficient amount in one day to get all of the nutrients they needed. For this reason, we had an extra set of molars to make the larger mouth more productive. This was particularly essential as the body lacked the ability to sufficiently digest cellulose. As evolution made its selections, our diets changed, our jaws grew appropriately smaller, and our third molars became unnecessary. Some human populations have now all but completely stopped growing wisdom teeth, while others have almost 100% likelihood of developing them.
3 Darwin’s PointPlica semilunaris
Darwin’s point is found in the majority of mammals, and humans are no exception. It is most likely used to help focus sounds in animals, but it no longer has a function in humans. Only 10.4% of the human population still has this visible left-over mark of our past, but it is possible that a much larger number of people carry the gene that produces it as it does not always cause the ear tubercle to appear. The point (shown in the picture above) is a small thick nodule at the junction of the upper and middle sections of the ear.
2Coccyx
The coccyx is the remnant of what was once a human tail. Over time we lost the need for a tail (as tree swinging was replaced by hanging out at the local water hole grunting neanderthal gossip), but we did not lose the need for the coccyx: it now functions as a support structure for various muscles and a support for a person when he sits down and leans back. The coccyx also supports the position of the anus.
1Appendix
The appendix has no known use in modern humans and is often removed when it becomes infected. While its original use is still speculated on, most scientists agree with Darwin’s suggestion that it once helped to process the cellulose found in the leaf-rich diet that we once had. Over the course of evolution, as our diet has changed, the appendix became less useful. What is particularly interesting is that many evolutionary theorists believe that natural selection (while removing all of the abilities of the appendix) selects larger appendices because they are less likely to become inflamed and diseased. So unlike the little toe, which may eventually vanish and is equally useless, the appendix is likely to stay with us for a long time – just hanging around doing nothing.
Embryology is an example of comparative anatomy as well - embryos go through stages of development, in vertebrates it appears that embryos show the relationships of ancestral pathways as they go through foetal development.
Link to diagram of vertebrate embryo's.
Who knew you had a fish stage in your embryo?
Link to some of these and some other examples of evolution happening in humans
http://www.sciencealert.com/watch-proof-of-evolution-that-you-can-find-on-your-own-body
4 Biochemical Evidence
- study of proteins, amino acids,genes and DNA that species that are closely related have in common, now that scientists are able to identify chemicals at these molecular levels they can work out close relationships between species based on their chemical differences. Close relatives have similar biochemicals.You can compare the genes located on the chromosomes of different species.
You can see the genes in common between this collection of primates, and can use the differences to establish how closely related the species are.
Studies of proteins like haemoglobin, of enzymes like cytochrome c, of immunoglobins can all show the relatedness between different species. Some proteins are so essential to life that they hardly mutate at all. These proteins are called Highly Conserved Proteins, and any change in an amino acid sequence can be traced.
Alan Wilson used these mutations to develop a Molecular Clock, which uses the rate of mutations to create a timeline for speciation. He showed that relationships between species could be constructed from changes in molecules such as proteins. The more changes there are, the further the distance in the relationship. Wilson used the sequences in the biological molecule to show that some species descend from common ancestors, the number of changes is related to time. He showed that Chimps and Humans have 99% the same sequences in our DNA, and that the time of separation from a common ancestor should be about 6 million years ago, and even more amazing, that all living humans descend from a single female ancestor that lived 60 000 years ago. (The Alan Wilson Centre is a world renowned research centre , and has excellent material about Human Evolution if you want to go there now)
New understandings from studies in this field are arriving all the time.
Scientists used to think that there was such a wide range of eye structures through out the animal kingdom that they must have developed independently. Studying genetics however has started to show that the genes for the structures of eyes are foundation genes, but how they turn on and what they do has evolved. There are some really exciting examples at this link to Learn Genetics Utah University Foundation Tool Kit genes page.
Basing an argument on Scientific Evidence is important - The theory of evolution uses separate lines of evidence from many fields to support the same argument, that species change due to natural observable processes. Stated Clearly gives some well made arguments. The video has the Same stuff that you have had in class, but a different voice to listen to.
Can fossils AND comparative anatomy both say the same thing. for example the evolution of whales.
Can complex structures like eyes actually evolve? Surely they are too hard or too soft to evolve? What about the half way eyes? Wouldn't those species just die out and not be present to evolve from? How can half working eyes give an evolutionary advantage and be successful? You'd think, but there is proof. Check out this doco, quite interesting so hang in there.
Conclusion
These are all ways that scientists have confirmed that evolution has been taking place. When you are thinking about species that might be evolving or might have evolved, your job is to think about which type of evidence can you use to find support for or against the idea that speciation has taken place.
An example of scientists using evidence to prove an evolutionary relationship is looking at teosinte corn, is it the ancestor of modern maize? What evidence would we need to find?
http://maize.uga.edu/index.php?loc=ancestors
Next job, how does evolution take place?
Mechanisms of Change
Sounds flash, but really it just means what is required to make a change in a species happen?The definition we have worked on in class is
'Evolution is a change in the allele frequency of a gene pool, over time'.
To cause evolution then, you must make a change in the allele's frequency. This just means make more of the allele or make less of the allele. If the allele becomes more or less common its frequency has changed. This change is identified as a micro evolutionary process (as compared to macro evolution which is speciation- evolution on a large scale - some people think they are the same thing just over different periods of time).
There are three main causes of change in allele frequency.
1 Natural Selection.
2 Migration.
3 Genetic Drift
A note about Mutation - without mutations you can't get different alleles for evolution to work on, so mutations are the foundation of evolution, but not a cause of change. What do you think? Is this splitting hairs?
This website gives a good animation explaining the mechanisms of change.
http://evolution.berkeley.edu/evosite/evo101/IIIBMechanismsofchange.shtml
And this website is a bit odd, the video of interest explains the features of Genetic Drift, there are a collection of videos that are a bit unpredictable, some are better than others, but the good ones are worth looking at,
a humourous lego simulation that explains the examples of Founder Effect, Bottlenecks and Genetic Drift really well
We need to look at case studies of each mechanism of change. yr 12 Bio go back to Genetic Variation and Change page.
Darwin's study of the natural environment led him to his theory.
http://videos.howstuffworks.com/science-channel/29147-100-greatest-discoveries-the-start-of-darwins-theory-video.htm
So in summary, natural selection is what Darwin is famous for writing down , it is the mechanism that makes sure the species is adapted to do well in the habitat they live in, genetic drift affects small populations, it is just a chance event that does not favour one phenotype over another to suit the habitat, and migration is migration, an individual arrives (or leaves) to breed with the members, bringing their alleles in (or out) of the pool.
All three make something happen that changes the balance between the alleles that are in the gene pool, from one generation to the next.
One key thing to remember is that the change has to be passed on to the next generation,if it isn't passed on to the gene pool of the next generation, it isn't evolution.
Try this interactive model where you choose the phenotype that is present, but the environment selects the fittest, your alleles might not be successful when the environment changes.
http://science.discovery.com/games-and-interactives/charles-darwin-game.htm
Genes and Chromosomes
This link is a great place to start with basic ideas http://learn.genetics.utah.edu/content/begin/tour/
Evolution relies on variation in a population. One of the main sources of variation is sexual reproduction. Sexual reproduction means that two parents contribute chromosomes to the offspring. For this to happen, reproducing adults must create a special cell with a half set of chromosomes. This sex cell is called a gamete. The process that creates a gamete is called Meiosis.
There are three features of meiosis and sexual reproduction that introduce this important variation.
1 Cross over and recombination
2 Independent assortment and segregation
3 Fertilisation of a gamete by another unique gamete.
Each of these steps needs to be clearly understood by students. So lets get some help.
Crossover is a process that only occurs in meiosis(not in mitosis). The homologous chromosomes must pair up in meiosis, and when they do, the chromatids that are lined next to each can overlap, and break off and recombine with the other chromatid. This swaps alleles from parents on to different chromosomes.
The original versions had alleles AB and ab, but after crossover one of the chromatids carries Ab, and the other carries aB. Now the offspring can get one of four possible combinations of these two alleles.
Which one it will get will depend on how the chromatids sort themselves into gametes.
Independent assortment and segregation.
This process happens independently for each pair of chromosomes, and every time it could be a different combo of chromosomes inside the gamete.
Whichever one of these gametes fertilises the other gamete,the offspring will be slightly different, but based on the same parents!
There are simple animations at this website. Open them in a new tab.
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#
Linked genes and Meiosis
Well explained at this youtube clip Andrew Douche teaches Linked genes.
And again, although a little old style video at Brainstorm